The invention relates to high purity fused silica glass. More particularly, the invention relates to loading high purity fused silica glass with molecular hydrogen. Even more particularly, the invention relates to a method of loading high purity fused silica glass with molecular hydrogen.
Fused silica glass is used in the semiconductor industry, forming optical components for photolithographic applications. Fused silica glass transmits at wavelengths of less than or equal to 250 nm and has a high level of optical homogeneity. Exposure to laser radiation at these short wavelengths, however, causes damage to the glass and shortens the lifetime of the optics. To increase the resistance of the glass to radiation damage, fused silica is loaded with molecular hydrogen (H2) using a diffusion process.
At high temperatures, hydrogen and silica react to form silicon hydride, which adversely affects laser damage performance, in the form of increased laser-induced wavefront distortion (LIWFD), and increased fluence dependent transmission (FDT). To minimize the effects of this reaction, hydrogen loading is usually carried out at temperatures of less than 500° C. Consequently, long loading times are needed to diffuse enough hydrogen into the glass to achieve acceptable H2 levels. Depending on the thickness of the part and the desired hydrogen distribution, hydrogen loading may take several months. Means to accelerate the hydrogen loading process, such as creating steep hydrogen gradients or using variable hydrogen surface concentrations, have been investigated.